1. Field of the Invention
The present invention relates generally to defective rigid data storage discs for use in hard disk drives and more particularly to a method for refinishing such defective discs.
2. Description of the Prior Art
Rigid data storage discs consist of a thin magnetically alterable coating adhered directly or indirectly to a relatively inflexible substrate having two planar surfaces. Typically the coating is of either a ferric oxide or a "magnetic nickel" film, while the substrate is usually aluminum.
Rigid data storage discs are commonly utilized in hard disk drives in conjunction with digital computers. The disc is the media upon which desired data is recorded and from which such data is retrieved. In hard disk drives the discs are mounted to rotate at relatively high speeds while read/write heads travel about the planar surfaces of the discs. The rotation of the disc creates air bushings about the planar surfaces of the discs. It is on these air bushings that the read/write heads float about the disc surfaces. The air bushings are very thin allowing the read/write heads to travel in close proximity to the surfaces of the discs.
Due to the nature of the air bushings the planar surfaces of the discs must be uniformly flat. Uneven disc surfaces result in the read/write head contacting the disc coating or "crashing" into the disc. Such "crashing" damages both the read/write head and the disc resulting in unacceptable disk drive performance.
Further, poor disk drive performance results if the coating is not uniformly applied onto the substrate or if the surfaces of the substrate have imperfections under the coating such as inclusions, pits, scratches, or other discontinuities. Discs with improperly applied coatings or with imperfect planar surfaces do not store or reproduce data in accordance with their design and are unacceptable for most computer data storage applications. Similarly, discs exhibiting roughness in the substrate surface or coating texture are unacceptable for most disk drive application.
Discs having coating or substrate imperfections are commonly known as "defective" discs. In some situations such discs may be recycled for future use if the defective coating or substrate surface imperfections can be eliminated and the substrate recoated. The preparation of a disc for recoating is referred to as "refinishing".
The inventors know of no comprehensive method in the prior art for refinishing rigid data storage discs that results in high yields of refinished discs suitable for recoating. The inventors are aware of a prior attempt to refinish rigid data storage discs by stripping the magnetically alterable coating from the disc using acid and then attempting to recoat the disc. Additionally, the inventors are aware of a prior effort to remove the magnetically alterable coating from the substrate via grinding operations. Both the acid removal refinishing process and the grinding process have numerous disadvantages.
One disadvantage with the prior art acid removal approach is that such results in etching or pitting of the substrate surface resulting in a decoated substrate unacceptable for recoating in the as-stripped condition.
Another disadvantage of the prior art acid removal approach is that it unpredictably leaves surface contaminants resulting in an inability to refinish such discs according to the teachings of the prior art.
Another disadvantage of the prior art acid approach is that it does not eliminate substrate surface unevenness resulting in defective discs even after recoating.
Another disadvantage of the prior art acid removal approach is that such does not eliminate substrate surface roughness resulting in defective discs after recoating.
A further disadvantage of the prior art in the use of the grinding method to remove the magnetically alterable disc coating is that it produces scratches, grooves and other surface irregularities in the substrate making its surfaces unacceptable for recoating.
A further disadvantage of the prior art grinding method is that it typically removes large quantities of substrate surface material reducing the thickness of the substrate below an acceptable thickness resulting in disc substrates unacceptable for recoating.
Another disadvantage of the prior art grinding method is that it leaves coated media on the outer edge of the disc resulting in the substrates not being suitable for recoating.
A further disadvantage of the prior art grinding method is that it produces disc substrates having improperly rounded edges unacceptable for recoating.
Another disadvantage of the prior art grinding method is that it does not produce stress-relieved substrate surfaces. Nonstress-relieved substrate surfaces can result in substrate flux causing an uneven substrate due to stress induced substrate warping. Uneven substrates are unacceptable for recoating.